Multilayer ceramic devices are known to include many various radio frequency (RF) packaging and devices. These multilayer ceramic devices are commonly found in electronic communication devices such as, cellular phones, two-way radios and wireless data devices. Some specific uses for multilayer ceramic devices may be found in transceiver antenna switches, voltage controlled oscillator modules and RF front end modules. Each of these applications requires side or bottom input/output (IO) pads on the multilayer ceramic in order to provide connections from the multilayer ceramic to a printed circuit (PC) board of the communication device.
Typically these IO pads are configured to form side metalization on the four or more vertical sides of a chip-shaped multilayer ceramic device along with contiguous bottom IO pads on the bottom portion of the ceramic device. Side metalization is used on the ceramic device to provide visibly reliable and mechanically robust solder connections when the device is surface mounted on a PC board. Upon reflowing, the solder can wick up the side metalization to provide a more reliable electrical and mechanical connection. Several methods have been developed to provide the side metalization for a wraparound electrical connection.
As shown in FIG. 1, one method is to use screen printing to paint a side connection trace 16 from an existing bottom trace 14 of a ceramic device 10 up a respective diced side 12 of the ceramic device 10 after the individual ceramic device 10 has been diced from a fired ceramic substrate array. This screen printing method is used because the process of dicing the individual ceramic devices exposes bulk non-metalized ceramic on the sides of each device. Many processing steps are involved in this method and many problems are observed. For example, each ceramic device is diced from a wafer array which means that wafer scale testing is not possible since side metalization is not available until after dicing. In addition the dicing process is very time consuming. Further, the side printing process is labor intensive because the individual diced ceramic devices have to be stacked and carefully aligned manually for screen printing.
As shown in FIG. 2 and 2A, another method to provide side metalization is to locate metal solid-filled vias 22 along singulation edges 24 of ceramic devices 20 in a ceramic array substrate 26 before firing (green state of the ceramic). Lines (shown as 24 in FIG. 2) are scribed in the substrate 26 along the vias 22 before firing to facilitate later singulation. After firing, each ceramic device is singulated from its substrate along the scribe lines 24 in the solid-filled vias 22 (shown in FIG. 2A). The subsequent split vias 28 serve as side connections 30 for each ceramic device 20. However, in this configuration individual device testing is not possible while in the array form since vias 22 are being shared between devices 20 until after they are singulated. This method disadvantageously does not allow for testing of individual devices while they are in the substrate array. Additionally, a clean splitting of the solid vias 22 can not be achieved reliably due to the mechanical strength difference between the ceramic and metal of the via. As a result, cracking occurs between the ceramic-metal interface of the via during the singulation action. Also, the surface of the side metalization tends to be very rough due to uneven pull-outs of the metal during singulation.
There is a need for a new method to provide reliable side input/output connections on a ceramic device, which: permits the use of array processing; allows testing of individual ceramic devices while in a substrate array form; utilizes conventional processing techniques; does not require a time consuming dicing operation; and provides a dimensionally uniform surface on the side metalization.
Accordingly, a ceramic device utilizing partial vias which have been scribed substantially therethrough while in the unfired green state would be an improvement over the prior art. A method which achieves reliable side metalization without requiring individualization of parts from their parent ceramic substrate array would also be an improvement over the art.